Cathode structure in a reflex klystron tube



Sept. 13, 1966 D. REVERDIN CATHODE STRUCTURE IN A REFLEX KLYSTRON TUBE 2 Sheets-Sheet 1 Filed June 15, 1962 MHz FIGJ

INVENTOR. Daniel REVERDIN I RN Y ATTO - Sept. 13, 1966 D. REVERDIN 3,273,004

CATHODE STRUCTURE IN A REFLEX KLYSTRON TUBE Filed June 15. 1962 2 Sheets-Sheet 2 FIG] n95 FIG.6

FIG. 6 FIGS FIG."

FIGJO Z I I NVENTOR Dania. REVERDIN -j mmc 9 T FIGJZ BY ATTORNZi' United States Patent 10 Claims. for. 313-310 The present invention relates to reflex klystrons, and aims at reducing the power hysteresis of electronic origin of a reflex klystron by means of a particular cathode structure.

Accordingly, it is an object of the present invention to provide a cathode structure for use with a reflex klystron which effectively reduces, by simple means, the power hysteresis effect that is normally encountered with reflex klystrons.

It is another object of the present invention to provide a cathode structure for reflex klystrons which minimizes the harmful effects of multiple transit of the electrons in reflex klystrons.

Still a further object of the present invention resides in the provision of a reflex klystron provided with a cathode of which the emissive surface thereof comprises a plurality of zones located at a predetermined distance from the grid in such a Way as to effectively eliminate the effects of multiple transit of the electrons.

A further object of the present invention resides in the provision of a reflex klystron structure provided with a particular cathode structure which is so arranged and constructed as to counteract the conditions causing the occurrence of parasitic modes of operations within the klystron tube.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, several embodiments in accordance with the present invention, and wherein FIGURES 1, 2 and 3 represent diagrams necessary for preliminary explanations relative to the present invention;

FIGURE 4 is an axial cross sectional view of a first embodiment of a cathode structure in accordance with the present invention;

FIGURE 5 is a plan view of the cathode structure of FIGURE 4;

FIGURE 6 is a plan view of a second embodiment of a cathode structure in accordance with the present invention;

FIGURE 7 is an axial cross sectional view through a third embodiment of a cathode structure in accordance with the present invention;

FIGURE 8 is a top plan view of the cathode structure of FIGURE 7;

FIGURE 9 is an axial cross sectional view through a fourth embodiment of a cathode structure in accordance with the present invention;

FIGURE 10 is a plan view of the cathode structure of FIGURE 9;

FIGURE 11 is an axial cross sectional view through a fifth embodiment of a cathode structure in accordance with the present invention; and

FIGURE 12 is a schematic cross sectional view through a reflex klystron.

It is known that in a reflex klystron, for a given tuning of the cavity and for a given anode voltage, the oscillation starts at a certain frequency within a mode which depends on the voltage applied to the reflector. It is 3,273,004 Patented Sept. 13, 1966 thus possible to determine the value of reflector voltage which corresponds to the maximum of power within the mode in question. By varying the reflector voltage about this value, one can cause the frequency to vary about the frequency which is given by the power maximum with the fixed tuning of the cavity. FIGURES 1 and 2 which illustrate diagrams of the power P of the klystron as a function of the absolute value of negative voltage of the reflector [V I show that the power within a given mode varies according to the curve ABC when the negative voltage of the reflector increases in absolute value. that is, when the frequency moves in a direction of increase. The ordinate DB corresponds to the power of the peak of the mode and at a certain frequency 1 which depends, on the one hand, on the tuning of the cavity and, on the other, on the anode voltage applied to the klystron.

There is also known in reflux klystrons the harmful phenomenon of power hysteresis, that is, the fact that the value of power is not unequivocal for a given value of reflector voltage. Thus, if after having described the curve ABC in the direction of increase of absolute value of V,-, one begins to decrease this value, the oscillation does not start at point C but at point E which may be located either ahead of (FIGURE 1) or behind (FIG- URE 2) the abscissa of the peak D. The power during return, therefore, does not describe the curve CBA, but instead the curve EFBA (FIGURE 1) or EFA (FIG- URE 2) either passing or not passing through the maximum amplitude as the case may be.

The hysteresis may be numerically described by its ratio which is defined in a different manner depending on whether the appearance of the phenomenon is that of FIGURE 1 or that of FIGURE 2.

In the case of FIGURE 1, the hysteresis ratio is given by the ratio of power at the moment of starting EF and the power at the peak of the mode BD, that is,

Consequently, this ratio may vary between 0 and In the case of FIGURE 2 the hysteresis ratio is given by the following equation: 7

Consequently, this ratio may vary between 100 and 200%.

It is known that the hysteresis depends at the same time on several causes, of which one of the most important is the effect of multiple transit of the electrons. This effect occurs when a portion of the electron beam emitted by the gun and reflected by the reflector field, once again traverses the grids of the tube returning toward the cathode surface in front of which it again reverses its direction and traverses the intergrid space for a third time. These reflected electrons may then start in oscillation of the same frequency as that which would be delivered by the klystron without this multiple transit but of opposite phase within the unfavorable conditions of the to and fro transit time thereof. If the amplitude thereof is sufficiently strong, the oscillation of the klystron is blocked and is not re-started except when these unfavorable conditions disappear with a sufiicient variation of the reflector voltage.

Since the hysteresis is harmful to the proper operation of the klystron, the present invention aims at reducing the same by seeking, in particular, to decrease the effect of multiple transit explained hereinabove.

According to the present invention, the reflex klystron is provided with a cathode of which the emissive surface comprises one or several zones located within a certain surface at a predetermined distance from the first grid, one or several other zones located within another surface at a predetermined distance from the preceding surface, and eventually one or several zones located within intermediate surfaces between the two preceding surfaces, or zones of progressive connection between these two surfaces.

The invention is based on the discovery of applicant according to which, if one plots a curve of variation of the hysteresis ratio 6 as a function of the frequency j, which is varied by tuning of the cavity with a constant anode voltage, one obtains a curve of the configuration shown in FIGURE 3 which has been derived from a particular klystron having an anode voltage V 950 v. and and tuned through frequencies of approximately 3,500 to 4,000 MHz, which may be considered as typical. This contour is characterized by a series of peaks a, b, separated by zones c having a relative minimum value of hysteresis ratio. These peaks are spaced according to the successive orders of the parasitic oscillation due to the multiple transit time, and correspond to the unfavorable conditions mentioned hereinabove, that is, to the conditions in which the parasitic mode acts in a destructive manner on the normal mode owing to a sufficiently important amplitude of the generated counter-oscillation. The zones of relative minimum correspond, in contrast, to the conditions in which the number of electrons which effectuate multiple transits is insufficient to produce this important amplitude but suflicient to produce an amplitude such that the starting of the oscillations produced by the electrons reflected by the reflector is nevertheless impaired. It is clear that the hysteresis effect is then less pronounced than at the frequencies in which the amplitude of the parasitic oscillation is at a maximum.

If now, all other things remaining the same, one varies the distance between the cathode and the first grid, the curve of FIGURE 3 is displaced parallelly to an extent that the peak a becomes peak a, and for a certain variation at of the cathode-grid distance, the peak a can be placed at the center between a and b, that is, where the hysteresis maximum replaces the minimum and vice versa. This distance d corresponds to a variation of the transit time of the electrons which from T becomes T such that in which T designates the period of oscillation at the frequency 1, that is, that the supplementary transit time of the electrons between the two cathode levels is equal to a half period of the started oscillation.

This relation permits calculation of the distance d which is approximately:

d 50v Vo in which d is in millimeters,

V in volts, and

f in Megahertz.

One thus conceives that if, according to the present invention, the cathode comprises at least one zone within a certain surface and at least another zone within a second surface, the distance between the two surfaces being equal to d, a portion of the electrons in course of multiple transit contributes to the maximum hysteresis whereas another portion contributes to the minimum. On the whole, the hysteresis will therefore have decreased at the frequencies at which its ratio presented previously a peak, and the curve of ratio as a function of the frequency is flattened and presents approximately the shape of the curve 0 shown in dot and dash line in FIGURE 3, the ratio maintaining a relatively slight value within the band of variation of frequency by means of the tuning of the cavity.

FIGURE 12 is a schematic cross-sectional view through a reflex klystron which includes a focalizing electrode 16, a resonator 17 having a rhumbatron cavity, a reflector cathode 18, and an outlet 19 coupled to the cavity. A cathode support is shown at 3 which supports any one of the cathode forms shown in FIGURES 4 to 11.

The variations in the constructional realization of the concept according to the present invention will be better understood by referring to the examples illustrated in FIGURES 4 to 11.

FIGURE 4 illustrates an axial cross sectional view and FIGURE 5 a plan view of a first embodiment in accordance with the present invention. In this embodiment, the cathode, secured on a support 3, comprises a first emissive layer 1 in the form of a plan or concave circular disc and a second emissive layer 2 which covers only a half circle of the preceding layer 1.

The distance between the planes or surfaces containing the free faces of the layers 1 and 2 is calculated according ot Equation 2 given hereinabove. For example, for V =1,000 v. and f=3,800 MHZ, one obtains d=0.4 millimeter approximately.

FIGURE 6 illustrates in plan view, analogous to FIG- URE 5, a second modified embodiment in accordance with the present invention. In the embodiment of FIGURE 6, the cathode disc is no longer subdivided into two half circles located in different planes, as in FIGURE 5, but into a certain number of sectors, for example, six sectors 4, 5, 6, 7, 8 and 9. The sectors 4, 6 and 8 then have the faces thereof located in the upper surface or plane, and the alternate sectors 5, 7 and 9 have the faces thereof located in the lower surface or plane. This embodiment may be readily realized by superposing supplemental sector-shaped emissive layers within the sectors 4, 6 and 8, over the emissive base disc disposed within the lower surface or plane. The distance between the two surfaces or planes is calculated as hereinabove.

According to FIGURES 7 and 8 which represent, respectively, an axial cross sectional View and a plan view of a third embodiment in accordance with the present invention, the zones at different levels are neither semi-circular nor sector-shaped as in the preceding examples but instead concentric. The cathode fixed on a support 3 comprises a circular emissive disc 11 provided at the center thereof with an embossment or depression 10. The difference in level between the depression 10 and the surface of the disc 11 is equal to d, calculated-as hereinabove. It is understood, however, that an analogous arrangement could be realized by placing a supplemental central layer having the dimensions of the circle 10 on the plane or concave circular disc 11.

In addition to the two levels spaced apart by a distance d defined as explained hereinabove, the cathode according to the present invention may also comprise any desired number of intermediate levels which has as its effect to further flatten the characteristics of FIGURE 3. It is thus that in a fourth embodiment, illustrated in axial cross section in FIGURE 9, and in plan view in FIGURE 10, the cathode is subdivided, for example, in three zones 12, 13 and 14 located at different levels, the assembly being fixed on a support 3 and being realized by superposition of successive emissive layers covering only a portion of the layer directly below. The difference of the outer levels of the layers 12 and 14 is equal to d, calculated as herein above.

By increasing the number of intermediate layers and by passing to the limit, one obtains a cathode reduced to a simple disc 14 fixed to a support 3 and inclined to the axis of the klystron 15 as shown in axial cross section in FIGURE 11. If the difference of levels between opposite rims of the disc is equal to d, calculated as hereinabove, this arrangement provides results substantially equivalent to the arrangements having separate stages as described hereinabove.

In the same manner, by providing sectors having intermediate levels in the disposition of FIGURE 6 and by increasing the number of levels, one could pass to the limit and replace the sectors formed by individual stages by progressive connecting surfaces which would impart to the cathode the aspect of a disc having fan-shaped foldings. It is understood that such cathodes are also comprised within the spirit and scope of the present invention.

While I have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto, but is susceptible of many changes and modifications within the spirit and scope thereof, as known to a person skilled in the art, and I therefore do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1. In a reflex klystron oscillator provided with a substantially axial direction, a primary electron source having at least one one first point and at least one second point of emissive surface, said first and second points being spaced in the axial direction of said klystron by a distance d substantially equal, in millimeters, to 50 /V /f, wherein V is the anode voltage in volts of said klystron, and f is the operating frequency in megacycles.

2. In a reflex klystron tube adapted to produce oscillatory energy by the electron flow of electrons emitted from a primary electron source, a primary electron source structure having emissive surface means for emitting said electrons, portions of said emissive surface means being disposed at least at two different levels, said two different levels being spaced from each other in the direction of electron flow by a predetermined distance such that the normal transit time of the electrons in said electron flow between said two levels is approxmiately equal to a halfcycle duration of the generated oscillation at a predetermined operating frequency, said spacing being substantially equal, in millimeters, to SOVV /f, where V is the anode voltage in volts, and f is said operating frequency in megacycles.

3. In a reflex klystron tube adapted to produce oscillatory energy by the electron flow of electrons emitted from a primary electron source, a primary electron source structure having emissive surface means vfor emitting said electrons, said emissive surface means being disposed at two different levels spaced in the axial direction of said klystron by a distance d substantially equal, in millimeters, to 50x/V /f, wherein V is the anode voltage in volts of said klystron, and f is the operating frequency in megacycles and including a body provided with an emissive surface and at least one sheet having a predetermined thickness and also provided with an emissive surface, said sheet being fixed to said body and the emissive surface area thereof being smaller than the emissive surface area of said body so as to cover only part thereof.

4. In a reflex klystron tube adapted to produce oscillatory energy by the electron flow of electrons emitted from a primary electron source, a primary electron source structure having emissive surface means for emitting said electrons, said emissive surface means being disposed at two different levels spaced in the axial direction of said klystron by a distance d substantially equal, in millimeters,

to 50x/V /f, wherein V is the anode voltage in volts of said klystron, and f is the operating frequency in megacycles and including a body provided with a substantially circular emissive surface and at least one sheet having a predetermined thickness and also provided with an emissive surface, said sheet being fixed to said body and the emissive surface area thereof being substantially semicircular so as to cover only part thereof.

5. In a reflex klystron tube adapted to produce oscillatory energy by the electron flow of electrons emitted from a primary electron source, a primary electron source structure having emissive surface means for emitting said electrons, said emissive surface means being disposed at two different levels spaced in the axial direction of said klystron by a distance d substantially equal, in millimeters,

to 50 /V /f, wherein V is the anode voltage in volts of said klystron, and f is the operating frequency in megacycles and including a body provided with an emissive surface and two sheets each at predetermined thickness and each provided with an emissive surface, said sheets being fixed effectively to said body and the emissive surface areas thereof being successively smaller than the emissive surface area of said body so as to define staged portions separated by mutually substantially parallel boundaries.

6. In a reflex klystron tube adapted to produce oscillatory energy by the electron flow of electrons emitted from a primary electron source, a primary electron source structure having emissive surface means for emitting said electrons, said emissive surface means being disposed at two different levels spaced in the axial direction of said klystron by a distance d substantially equal, in millimeters,

to 50 /V /f, wherein V is the anode voltage in volts of said klystron, and f is the operating frequency in megacycles and including a body provided with an emissive surface and at least one sheet of sectoral shape having a predetermined thickness and also provided with an emissive surface, said sheet being fixed to said body and the emissive surface area thereof being smaller than the emissive surface area of said body so as to cover only part thereof.

7. In a reflex klystron tube adapted to produce oscillatory energy by the electron flow of electrons emitted from a primary electron source, a primary electron source structure having emissive surface means for emitting said electrons, portions of said emissive surface means being disposed at two different levels spaced in the axial direction of said klystron by a distance 01 substantially equal, in millimeters, to S0 /V /f, wherein V is the anode voltage in volts of said klystron, and f is the operating frequency in megacycles and being substantially concentric to each other.

8. In a reflex klystron tube adapted to produce oscillatory energy by the electron flow of electrons emitted from a primary electron source, a primary electron source structure provided with a depression in the central area thereof and having emissive surface means for emitting said electrons, portions of said emissive surface means being disposed at two different levels spaced in the axial direction of said klystron by a distance d substantially equal, in millimeters, to 50 /V /f, wherein V is the anode voltage in volts of said klystron, and f is the operating frequency in megacycles and being substantially concentric to each other.

9. In a reflex klystron oscillator having an axial direction, a primary electron source structure provided with a substantially planar emissive surface inclined with respect to said axial direction and operable to emit electrons adapted to form an electron flow in said axial direction, the distance, in the axial direction of the klystron, between two diametrically opposite points of the periphery of the primary electron source structure being such that the transit time of the electrons in said electron flow along said distance is substantially equal to a half-cycle duration of the generated oscillation at a predetermined oscillatory frequency, said distance being substantially equal, in millimeters, to SO V wherein V is the anode voltage in volts of said klystron, and f is said operating frequency in megacycles.

10. In a reflex klystron tube adapted to produce oscillatory electromagnetic wave energy by the to and fro movements of electrons in an electron stream and including a primary electron source structure provided with emissive surface means for emitting said electrons and with means for producing said electron flow including the to and fro 7 8 movements thereof in predetermined transit time, the References Cited by the Examiner improvement essentially consisting of means for reducing UNITED STATES PATENTS the power hysteresis in said klystron by minimizing cer- 2,518,954 8/ 1950 Steele 3155.22 tain parasitic oscillations due to the multiple transit of the 2,604,605 7/ 1952 Varian 3155 .22 electron flow including means for emitting from said pri- 5 ,7 5,499 11/ 1955 Field 3153.6 mary electron source structure electrons at two points FOREIGN PATENTS spaced 1n the direction of the multiple transit by a distance 937,351 12/1946 France.

d substantially equal, in millimeters, to SOVT' /f, wherein HE the V is the anode voltage in volts of said klystron, and JOHN HUC r 'f f is the operating frequency in megacycles. 10 JAMES D. KALLAM, Assistant Examine). 

1. IN A REFLEX KLYSTRON OSCILLATOR PROVIDED WITH A SUBSTANTIALLY AXIAL DIRECTION, A PRIMARY ELECTRON SOURCE HAVING AT LEAST ONE ONE FIRST POINT AND AT LEAST ONE SECOND POINT OF EMISSIVE SURFACE, SAID FIRST AND SECOND POINTS BEING SPACED IN AN AXIAL DIRECTION OF SAID KLYSTRON BY A DISTANCE D SUBSTANTIALLY EQUAL, IN MILLIMETERS, TO 50$VO/F, WHEREIN VO IS THE ANODE VOLTAGE IN VOLTS OF SAID KLYSTRON, AND F IS THE OPERATING FREQUENCY IN MEGACYCLES. 